1. Field of the Invention
The present invention relates generally to a hydraulically and pneumatically operated shock absorber for vehicles.
2. Description of the Prior Art
Hydraulic shock absorbers which are widely used comprise a hydraulic damper and a spring operatively combined therewith. Such prior shock absorbers provided with a spring provide a dampening characteristic which is commensurate with an applied force, and have a property not suitable for vehicles of certain types. By including a spring, the diameter of the shock absorbers must be enlarged and the size thereof made greater than would otherwise be necessary. Further, the shock absorbers are heavy due to addition of the spring and associated parts, and are complicated in structure. An additional problem with the shock absorbers described above is that spring-loading adjustment is relatively difficult, thereby producing irregularly spring-loaded shock absorber products.
There has been proposed a hydraulically and pneumatically operated shock absorber which utilizes a pneumatic spring. The shock absorber of this type solves the above-mentioned difficulties in that it maintains an increased degree of response during the compression stroke and is hydraulically controlled to produce a large dampening force while in the extension stroke. The pneumatic spring type of shock absorber is especially suitable for automobiles for use on roads with many holes and bumps, requiring shock absorbers which have a long compression stroke and rapid responsiveness.
The hydraulically and pneumatically operated shock absorber includes an air chamber and a fluid chamber which are generally divided by a free piston. Such partitioning, however, results in difficulty in sealing between the chambers, and the piston itself is not smoothly and reliably slidable.
Various efforts have been made to eliminate the above-discussed defects. As a result, different types of flexible and resilient members have been proposed for use as a partition between the air and fluid chambers. One such type comprises a disc-shaped flexible partition member which separates a compartment in an upper portion of the shock absorber body into upper and lower parts. With this type of partition member, however, the shock absorber becomes greater in overall length and larger in size. In addition, attachment and centering of the flexible partition member involves complex processes. Another type of partition member is composed of a similar disc-shaped flexible separator which is vertically arranged as a partition for a chamber mounted on a side of the shock absorber body. This latter type causes the structure of the shock absorber to be relatively complicated and large-sized. Further, it suffers from the same problems as the former type in connection with attachment and centering.
Another type of hydraulic and pneumatic shock absorber comprises inner and outer telescoping tubes, the inner tube having at its one end a partition member having an orifice and the outer tube being equipped with a tapered rod with a piston fixed thereto having an orifice. The fluid can be forced to pass through one of the orifices during either the compression or the extension stroke, the orifice with which the rod interferes being variable by relative movement of the inner and outer tubes. One of the problems attendant such shock absorber is that when the shock absorber is subjected to lateral bending forces while it is at the end of the extension stroke with the piston in abutment against the partition member and with the sliding parts of the inner and outer tubes becoming closer to each other, the cross-sectional shape of a clearance defined between the rod and the orifice wall becomes irregular. Thus, oil is caused to flow irregularly through the deformed cross-sectional shape of the orifice on the compression stroke, with the consequence that the shock absorber will not function properly. This difficulty also arises when the shock absorber is in the vicinity of the end of the extension stroke. Other problems include: the rod is frictionally engageable with the orifice wall; and the piston, rod and inner tube are subjected to stresses, preventing smooth and reliable shock absorbing operation.
Furthermore, with this latter type of shock absorber, there are three points of contact; one between upper sliding surfaces of the inner and outer tubes, one between lower sliding surfaces of the tubes, and one between sliding surfaces of the inner tube and the piston. Thus, one extra point of contact is provided as compared with other conventional shock absorbers. Accordingly, if the parts are made of rigid material, they will be subjected to severe stresses, especially when side forces in addition to axial forces are applied to the shock absorbers, thereby impeding smooth operation. Because the rod is relatively slender, it can be easily bent when the piston is held by the inner tube with the rod fixedly supported by the outer tube. At this time, irregular stresses are created on the sliding surface of the piston, thus preventing the piston from being able to slide smoothly. Such a condition can cause the rod to be deformed, and when repeated, may even break a piston supporting portion on the tube. The service life of the shock absorber may then be shortened, and the durability thereof lessened.
The present invention provides a shock absorber of improved performance which eliminates the above discussed various problems attendant the shock absorbers of the conventional type and of the hydraulic and pneumatic type.